Within the field of computing, many scenarios involve the storage of data on one or more nonvolatile storage devices (e.g., platter-based magnetic and/or optical hard disk drives, solid-state storage devices, and nonvolatile memory circuits). Many details of the data storage may vary, such as the word size, the addressing method, the partitioning of the storage space of the storage device into one or more partitions, and the exposure of allocated spaces within the storage device as one or more volumes within a computing environment.
In many such storage scenarios, techniques may be utilized to detect unintended changes to the data. For example, an error in the reading or storing logic of the device, a buffer underrun or overrun, a flaw in the storage medium, or an external disruption (such as a cosmic ray) may occasionally cause an inadvertent change in the data stored on the storage medium or in the reading of data from the storage medium. Therefore, in many such scenarios, the data is stored on the storage devices according to an error detection scheme involving a verifier (e.g., a parity bit or checksum) computed for respective data sets (e.g., different words, sectors, regions, or other sets of data). The verifier may be used to confirm that the contents of the data set have been validly stored to and/or read from the storage device. As one such example, in the context of storing a data set comprising a set of bits, an exclusive OR (XOR) operation may be applied to the bits, resulting in a parity bit that may be stored and associated with this data set. When the data set is later read, another XOR operation may be applied thereto, and the result may be compared with the parity bit. A change of any one bit results in a mismatch of these XOR computations, indicating that the data has been incorrectly stored, altered, or incorrectly read from the storage device. Many types of verifiers may be identified, which may vary in some features (e.g., ease of computation, a capability of identifying which bit of the data set has changed, and an error-correction capability whereby an incorrectly read portion of data may be corrected).
Error detection schemes are often utilized in Redundant Array of Inexpensive Disks (RAID) arrays, such as a set of hard disk drives that are pooled together to achieve various aggregate properties, such as improved throughput and automatic data mirroring. As one such example, a RAID 4 array involves a set of two or more disks, where one disk is included in the array not to store user data, but to store verifiers of the data stored on the other disks. For example, for a RAID 4 array involving four disks each storing one terabyte of data, the capacity of the first three disks is pooled to form a three-terabyte storage space for user data, while the fourth disk is included in the array to hold verifiers for data sets stored on the first three disks (e.g., for every three 64-bit words respectively stored on the other three disks, the fourth disk includes a 64-bit verifier that verifies the integrity of the three 64-bit words). The RAID array controller comprises circuitry that is configured to implement the details of a selected RAID level for a provided set of drives (e.g., upon receiving a data set, automatically apportioning the data across the three user data disks, calculating the verifier of the data set, and storing the verifier on the fourth disk). The RAID techniques used may also enable additional protections or features; e.g., if any single storage device in a RAID 4 array fails, the data stored on the failed device may be entirely reconstructed through the use of the remaining storage devices.